Two rebel groups active in the Democratic Republic of Congo's restive east, the M23 and FDLR, have formed an alliance and clashed with the country's military, an army spokesman said Wednesday.

Lieutenant-Colonel Olivier Hamuli said the M23, a rebel group formed by army mutineers who have been battling with their former colleagues and sowing terror in the east, had teamed up with the Democratic Forces for the Liberation of Rwanda (FDLR) in a bid to gain more territory in the region.

"Clashes began on Wednesday morning. These are M23 elements allied with the FDLR," Hamuli said. "They were fought off."

The M23 was formed in April by former fighters in the National Congress for the Defence of the People (CNDP), an ethnic Tutsi rebel group that was integrated into the army under a 2009 peace deal whose terms the mutineers claim were never fully implemented.

The FDLR's members are ethnic Hutus who were soldiers in the Rwandan army before being forced out of the country in the wake of the 1994 genocide, which killed 800,000 people -- mostly Tutsis.

M23 spokesman Vianney Kazarama denied that the group had formed an alliance with the FDLR.

The United Nations has accused the Rwandan military of backing the M23, a charge Kigali denies.